| Message ID | 20220110181546.4131853-3-farosas@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | target/ppc: powerpc_excp improvements [40x] (3/n) | expand |
On Mon, Jan 10, 2022 at 03:15:40PM -0300, Fabiano Rosas wrote: > Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com> > --- > target/ppc/cpu_init.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c > index a50ddaeaae..9097948e67 100644 > --- a/target/ppc/cpu_init.c > +++ b/target/ppc/cpu_init.c > @@ -1951,7 +1951,9 @@ static void init_excp_4xx_softmmu(CPUPPCState *env) > env->excp_vectors[POWERPC_EXCP_EXTERNAL] = 0x00000500; > env->excp_vectors[POWERPC_EXCP_ALIGN] = 0x00000600; > env->excp_vectors[POWERPC_EXCP_PROGRAM] = 0x00000700; > + env->excp_vectors[POWERPC_EXCP_FPU] = 0x00000800; I have a vague recollection from my days of working on 405 that there may have been something funky with FP emulation on there: e.g. FP instructions causing 0x700 program interrupts instead of FP unavailble interrupts or something. I might be remembering incorrectly - the manual does seem to imply that 0x800 FP unavailable is there as normal, but it might be worth double checking this (against real hardware, if possible). > env->excp_vectors[POWERPC_EXCP_SYSCALL] = 0x00000C00; > + env->excp_vectors[POWERPC_EXCP_APU] = 0x00000F20; > env->excp_vectors[POWERPC_EXCP_PIT] = 0x00001000; > env->excp_vectors[POWERPC_EXCP_FIT] = 0x00001010; > env->excp_vectors[POWERPC_EXCP_WDT] = 0x00001020;
David Gibson <david@gibson.dropbear.id.au> writes: > On Mon, Jan 10, 2022 at 03:15:40PM -0300, Fabiano Rosas wrote: >> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com> >> --- >> target/ppc/cpu_init.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c >> index a50ddaeaae..9097948e67 100644 >> --- a/target/ppc/cpu_init.c >> +++ b/target/ppc/cpu_init.c >> @@ -1951,7 +1951,9 @@ static void init_excp_4xx_softmmu(CPUPPCState *env) >> env->excp_vectors[POWERPC_EXCP_EXTERNAL] = 0x00000500; >> env->excp_vectors[POWERPC_EXCP_ALIGN] = 0x00000600; >> env->excp_vectors[POWERPC_EXCP_PROGRAM] = 0x00000700; >> + env->excp_vectors[POWERPC_EXCP_FPU] = 0x00000800; > > I have a vague recollection from my days of working on 405 that there > may have been something funky with FP emulation on there: e.g. FP > instructions causing 0x700 program interrupts instead of FP unavailble > interrupts or something. Maybe this (from the manual): Program - causing conditions: Attempted execution of illegal instructions, TRAP instruction, privileged instruction in problem state, or auxiliary processor (APU) instruction, or unimplemented FPU instruction, or unimplemented APU instruction, or APU interrupt, or FPU interrupt FPU Unavailable - causing conditions: Attempted execution of an FPU instruction when MSR[FP]=0. There's also this bit: Attempted execution of an APU instruction while the APUc405exception signal is asserted) results in a program interrupt. Similarly, attempted execution of an FPU instruction whilethe FPUc405exception signal is asserted) also results in a program interrupt. The following also result in program interrupts: attempted execution of an APU instruction while APUc405DcdAPUOp is asserted but APUC405DcdValidOp is deasserted; and attempted execution of an FPU instruction while APUc405DcdFpuOp but APUC405DcdValidOp is deasserted. > I might be remembering incorrectly - the manual does seem to imply > that 0x800 FP unavailable is there as normal, but it might be worth > double checking this (against real hardware, if possible). The Linux kernel has the vectors that I'm adding disabled: EXCEPTION(0x0800, Trap_08, unknown_exception) <-- FPU EXCEPTION(0x0900, Trap_09, unknown_exception) EXCEPTION(0x0A00, Trap_0A, unknown_exception) EXCEPTION(0x0B00, Trap_0B, unknown_exception) ... EXCEPTION(0x0F00, Trap_0F, unknown_exception) <-- APU (0xf20 would probably cause a crash as we'd jump to the middle of the exception prologue) Maybe I should drop this patch then? That way future developers won't feel tempted to raise one of these. It seems mostly inconsequential either way, what do you think?
On Fri, Jan 14, 2022 at 06:46:10PM -0300, Fabiano Rosas wrote: > David Gibson <david@gibson.dropbear.id.au> writes: > > > On Mon, Jan 10, 2022 at 03:15:40PM -0300, Fabiano Rosas wrote: > >> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com> > >> --- > >> target/ppc/cpu_init.c | 2 ++ > >> 1 file changed, 2 insertions(+) > >> > >> diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c > >> index a50ddaeaae..9097948e67 100644 > >> --- a/target/ppc/cpu_init.c > >> +++ b/target/ppc/cpu_init.c > >> @@ -1951,7 +1951,9 @@ static void init_excp_4xx_softmmu(CPUPPCState *env) > >> env->excp_vectors[POWERPC_EXCP_EXTERNAL] = 0x00000500; > >> env->excp_vectors[POWERPC_EXCP_ALIGN] = 0x00000600; > >> env->excp_vectors[POWERPC_EXCP_PROGRAM] = 0x00000700; > >> + env->excp_vectors[POWERPC_EXCP_FPU] = 0x00000800; > > > > I have a vague recollection from my days of working on 405 that there > > may have been something funky with FP emulation on there: e.g. FP > > instructions causing 0x700 program interrupts instead of FP unavailble > > interrupts or something. > > Maybe this (from the manual): > > Program - causing conditions: > > Attempted execution of illegal instructions, TRAP instruction, > privileged instruction in problem state, or auxiliary processor (APU) > instruction, or unimplemented FPU instruction, or unimplemented APU > instruction, or APU interrupt, or FPU interrupt > > FPU Unavailable - causing conditions: > > Attempted execution of an FPU instruction when MSR[FP]=0. > > There's also this bit: > > Attempted execution of an APU instruction while the APUc405exception > signal is asserted) results in a program interrupt. Similarly, attempted > execution of an FPU instruction whilethe FPUc405exception signal is > asserted) also results in a program interrupt. The following also result > in program interrupts: attempted execution of an APU instruction while > APUc405DcdAPUOp is asserted but APUC405DcdValidOp is deasserted; and > attempted execution of an FPU instruction while APUc405DcdFpuOp but > APUC405DcdValidOp is deasserted. Right... those do seem to suggest that FP comes in as a 0x700 rather than 0x800. Really hard to be sure without checking an actual chip. > > I might be remembering incorrectly - the manual does seem to imply > > that 0x800 FP unavailable is there as normal, but it might be worth > > double checking this (against real hardware, if possible). > > The Linux kernel has the vectors that I'm adding disabled: > > EXCEPTION(0x0800, Trap_08, unknown_exception) <-- FPU > EXCEPTION(0x0900, Trap_09, unknown_exception) > EXCEPTION(0x0A00, Trap_0A, unknown_exception) > EXCEPTION(0x0B00, Trap_0B, unknown_exception) > ... > EXCEPTION(0x0F00, Trap_0F, unknown_exception) <-- APU > > (0xf20 would probably cause a crash as we'd jump to the middle of the > exception prologue) Right.. that's fairly strong evidence that those vectors don't operate in practice. > Maybe I should drop this patch then? That way future developers won't > feel tempted to raise one of these. Maybe. Better yet would be to verify on a chip then drop a comment in there explicitly describing the situation > It seems mostly inconsequential either way, what do you think? Well, yes.
diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c index a50ddaeaae..9097948e67 100644 --- a/target/ppc/cpu_init.c +++ b/target/ppc/cpu_init.c @@ -1951,7 +1951,9 @@ static void init_excp_4xx_softmmu(CPUPPCState *env) env->excp_vectors[POWERPC_EXCP_EXTERNAL] = 0x00000500; env->excp_vectors[POWERPC_EXCP_ALIGN] = 0x00000600; env->excp_vectors[POWERPC_EXCP_PROGRAM] = 0x00000700; + env->excp_vectors[POWERPC_EXCP_FPU] = 0x00000800; env->excp_vectors[POWERPC_EXCP_SYSCALL] = 0x00000C00; + env->excp_vectors[POWERPC_EXCP_APU] = 0x00000F20; env->excp_vectors[POWERPC_EXCP_PIT] = 0x00001000; env->excp_vectors[POWERPC_EXCP_FIT] = 0x00001010; env->excp_vectors[POWERPC_EXCP_WDT] = 0x00001020;
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com> --- target/ppc/cpu_init.c | 2 ++ 1 file changed, 2 insertions(+)